Neuromuscular blocking agents are powerful drugs that are being used with increasing frequency in critical care medicine. The choice of a particular muscle relaxant is influenced by the patient's underlying condition and the side-effects of the drugs. Many factors influence an individual's response to neuromuscular blocking agents, and therefore, each patient's response should be monitored with a nerve stimulator. When muscle relaxants are used, common complications are patient awareness secondary to inadequate analgesia and sedation, and overdose of the neuromuscular blocking agents. Prolonged paralysis for days to weeks after the discontinuation of neuromuscular blocking agents is an uncommon but devastating complication, the etiology of which is poorly understood. Physicians in critical care medicine should receive formal training in the use of neuromuscular blocking drugs.